1. Field of the Invention
The present invention relates to a method of fabricating a nonvolatile memory device. In particular, the present invention relates to a method of fabricating a nonvolatile memory device having enhanced electrical characteristics.
2. Description of the Related Art
In general, nonvolatile memory devices, e.g., read only memory (ROM), refer to semiconductor devices that can retain data permanently, i.e., when the power supply is turned off. Accordingly, nonvolatile memory devices may be widely used in various fields.
Nonvolatile memory devices may be classified according to types of memory storage layers employed in a unit cell thereof, i.e., floating-gate type nonvolatile memory devices and charge-trapping type nonvolatile memory devices. Recently, development of charge-trapping type nonvolatile memory devices has increased due to their low power consumption and high integration capabilities.
The conventional charge-trapping type nonvolatile memory device may be classified as a silicon-oxide-nitride-oxide-silicon (SONOS) device or as a metal-oxide-nitride-oxide-silicon (MONOS) device. Further, the conventional charge-trapping type nonvolatile memory device may include charge tunneling layers, charge trapping layers for injecting and retaining electric charges, and charge blocking layers above the charge trapping layers. The charge blocking layers may be formed of metal oxide materials at a reduced thickness to improve high density integration and reduce leakage current thereof.
However, formation of metal oxide layers may require large amounts of ozone (O3), thereby triggering potential oxidation of layers that are in communication therewith, e.g., the charge trapping layers. Consequently, oxide layers may be formed on interfaces between the charge trapping layers and the charge blocking layers, thereby deteriorating threshold voltage window (Vth window) characteristics of the nonvolatile memory device.
Accordingly, there exists a need for an improved method of forming a nonvolatile memory device having a metal oxide charge blocking layer exhibiting enhanced threshold voltage window characteristics.